The Persians, like other Indo-European groups such as the Medes and Scythians were originally polytheists. They worshipped numerous gods associated with natural phenomena such as the moon and the sun, fire, wind and water. Their religious practices included, animal sacrifice, a reverence for fire and the drinking of a natural intoxicant made from the juice of the haoma plant.
Around 600 B.C. the prophet and teacher Zoroaster, founded a new religion, Zoroastrianism. Zoroaster, also known by the Greek name Zarathrustra, wrote down his beliefs in a sacred book known as the "Zend Avesta".
Zoroastrianism was a monotheistic religion. Zoroaster taught that there was only one God, Ahura Mazda or 'wise Lord', the source of all creation. The Perians were one of the first people to become monothesists, Darius I (552-486 B.C.) is thought to be the first Achaemenid king to convert to Zoroastrianism. His predecesors, Cyrus the Great and his son Cambyses, are believed to have followed the traditional Indo-European beliefs of their ancestors.
Under Zoroastrianism, earlier Persian customs and beliefs in deities or spirits were not totally replaced. These deities were relegated to the status of demons or daevas which were in opposition to the ahuras.
The monotheism of early Zoroastrianism however was to undergo some changes. Its dualistic view of the world as life being a struggle between good and evil developed under later Zoroastriam, into the struggle of "Ahura Mazda" (light) representing goodness, with "Ahriman" (Darkness) representing evil.
It was to develop still further in Jewish and Christian religions into concepts of heaven and hell. This is only one of many concepts of the Zoroastrian religion that was integrated into the religious beliefs of the Jewish people.
Other developments in Zoroastrianism saw the reemergence of minor deities such as Mithra and Anahita who regained some of their prominence, particularly during the reign of Artaxerxes II.
Many believe the three wisemen were Zoroastrian priests.
Zoroaster stressed the need to act righteously and to speak the truth. He condemned the practice of animal sacrifice, and elevated to central importance of fire as a symbol of truth. Herodotus decribed the Persian's religious practice: "they have no images of the gods, no temples nor altars"
From Darius I onwards, the god Ahuramazda or its representation began to be pictured above the Persian Kings on seals and reliefs. The symbol was a combination of several symbols, it combined the wings and body of the falcon and a crowned miniature of the King joined to the falcon by a ring. However the representation is thought not to be the god 'Ahuramazda', but rather a sign of his blessing or authority. The divine Ahuramazda could not be pictured, the blessing is associated with the wealth and success of the King and his divine right to rule. The ring, symbolising the bond between man and heaven.
In the Avesta, god's grace manifests itself as a falcon. The winged disc symbol also appeared in Assyrian art and as a representation of the Egytian God Horus.
There was considerable change in the religion during the time of Zoroaster and throughout the period of Achaemenid Persia. It is possible that changes to Zoroastrianism may have sparked conflicts among the royal Achaemenids.
The Achaemenian kings respected and officially accepted the various religions of the different city states in the conquered terriories without imposing Zoroastrianism.
Zoroastrian was continued under the Parthians and finally under Sassanid rule. After the Arab invasion, many of the faithful fled to India and became known as the Parsi.
